[Alneyan]

It is true enough that there is little difference between the three weapons; so long as you do something useful with them, they will all get the job done. Going straight for APB gives a lead of a few turns (three perhaps?), which is unlikely to matter much. After all, a MB/PBB user should research the first few levels of APB in the meantime, given how cheap these are.

The strength of the APBs I have forgotten to mention is their added range compared to PPB/MB (from APB VII or VIII; I don't recall which). If you have half-decent chances to hit at range 7, mainly for lack of Stealth/Scattering Armour s, then having a better range can help. It isn't a game-breaking factor however; but then, few weapons choices can be argued to alter the course of a game.

To answer the original query: I go to DUC IV and then APB VII/VIII (the one with range 7) as soon as possible, unless I believe shields will be widely used early on. If nothing out of the ordinary happens, APB XII/Shield Depleters are standard afterwards, with eventually the Wave Motion Gun. If the Crystalline Armour and/or the Talisman are detected, the emergency plan is set into motion to try to save my hide, and all of the above is scrapped. Somehow, these Torpedoes sure look attractive when under attack by a Crystalline Empire.